iio: adc: tsc2046: fix scan interval warning

Sync if statement with the actual warning.

Fixes: 9504db57 ("iio: adc: tsc2046: fix a warning message in tsc2046_adc_update_scan_mode()")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20211007093007.1466-2-o.rempel@pengutronix.de


Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>